Hydrocarbon fuels having improved anti-knock properties



Un e Sm This invention relates to motor fuels for use in sparkignition engines. More particularly, it relates to improvements in anti-knock characteristics of such motor fuels containing organo-lead anti-knock agents. 7

Organo-lead compounds, and especially tetraethyl lead, are widely used as anti-knock addition agents in motor fuels formulated for use in spark-ignition engines. However, often the organo-lead compounds lose a certain amount of their anti-knock effectiveness under combustion chamber conditions in spark-ignition internal combustion engines. This is particularly true in motor fuels containing increased amounts of aromatic hydrocarbon constituents. Such motor fuels containing more and more aromatic hydrocarbons have come into common usage in recent years to satisfy the high octane requirements of modern engines. Additionally, the higher compression engines of recent development have increased the antiknock requirements of motor fuels. Aromatic-rich motor fuels, in spite of their high octane indexes, show less response to organo-lead compounds, such as tetraethyl lead, than the parafiinic constituents. Also, the amount of organo-lead anti-knock compound includable in motor fuels is limited by regulation; and, in addition, the cost of such anti-knock compounds makes it desirable to increase the anti-knock effectiveness of a given amount of antiknock agent.

In recent years, it has been discovered that the effectiveness of organo-lead anti-knock compounds can be increased by using addition agents capable of exerting some beneficial efiect on the organo-lead anti-knock agent. Such supplementary compositions for use with organolead anti-knock agents have become known as lead appreciators."

While it is not intended to be held to any theories regarding knock suppression by anti-knock agents, it is believed that in the case of organo-lead anti-knock agents the organo-lead compound is converted in the combustion chamber to an active form of lead oxide, a form effective in suppressing knock, The active form of lead oxide is often converted to an inactive form of lead oxide which is believed to exist in large particle sizes. This latter conversion is believed to take place in the flame front during combustion and results in decreasing the activity of the organo-lead compound. The lead appreciators apparently exert some action under combustion chamber conditions upon the inactive form of lead oxide and convert such lead oxide to a complex or compound, which is then decomposed to form the active form of lead oxide, which is then available for anti-knock suppression.

It is an object of this invention to provide appreciators for use with organo-lead anti-knock compounds and, particularly, tetraethyl lead. Another object is to provide leaded motor fuel compositions of increased antiknock characteristics and, particularly, such motor fuel compositions wherein the b'ase motor fuel is rich in aromatic hydrocarbon constituents. A further object is to provide 3,160,485 Patented Dec. 8, 1964 "ice improvement in the anti-knock action of motor fuels containing tetraethyl lead under operating spark-ignition engine combustion chamber conditions. Other objects will be apparent to those skilled in the art from the following description.

It has been discovered that the Research octane number of leaded aromatic-rich gasolines containing at least 20 volume percent aromatic hydrocarbons and having a Research octane number of at least is markedly improved by the addition of a synergistic additive combination of naphthenic acid and lithium naphthenate.

The high octane hydrocarbon motor fuel of this invention comprises aromatic-rich gasoline containing at least 20 volume percent aromatic hydrocarbons, an organolead anti-knock agent, naphthenic acid and lithium naphthenate.

The naphthenic acid must be present in amounts be tween 0.05 to 1.0 volume percent in order to realize synergistic lead appreciation with lithium naphthenateand concomitant Research octane number increase in the leadedaromatic-rich motor fuel compositions of the invention. 'The preferred concentration of naphthenic acid in the synergistic additive falls between 0.1 to 1.0 volume percent with maximum results generally'being obtained at a concentration level of about 0.5 volume percent. Concentrations of naphthenic acid above volume per-. cent can be incorporated in the fuel compositions, but such concentrations adversely aifect the synergistic action.

Naphthenic acids suitable for use in this invention are complex mixtures of carboxylic acids which occur naturally in variou s'crude petroleum oils, usually in propor tions below 1 percent, and which may be extracted therefrom by the use of alkalies. Extensive research has demonstrated that petroleum naphthenic acids fall into at least three general categories: (1) aliphatic acids having the general formula C H O and predominating in compounds wherein n is 6 to 7, (2) acids having the general formula C H O and shown to be cyclopentane derivatives C H l(CH CO H, where x generally varies from 1 to about 4 and wherein the cyclopentane ring may also contain one or more alkyl groups, (3) acids having the general formula C l-l iO known to contain a bicyclic cycloaliph atic nucleus and containing about 12 to 25 carbon atoms. The above classification presents a somewhat over-simplified picture. Some evidence has been adduced of the existence of even more complex acids in petroleum naphthenic acids, including triand tetra-cyclic cycloaliphatic-substituted' aliphatic carboxylic acids. There is evidence that the molecular weights in the above classes overlap; thus, although the simple aliphatic acids preacids obtained from petroleum can be suitably employed.

The lithium riaphthenate must be present in an amount sufficient to provide from 0.01 to 2.5 grams of lithium per gallon of fuel in order torealize synergistic lead appreciation with naphthenic acid and concomitant Research octane number increase in the leaded aromatic-rich motor fuels ofthe invention. Thepreferred range being between 0.25 to 1.5 grams of lithium per gallon. The amount employed will of course vary with the quality and the intended end use of the fuel.

In general, the lithium naphthenate employed in this invention can be prepared by reacting a naphthenic acid with lithium or lithium hydride, hydroxide, alkoxide or carbonate. The lithium naphthenate is readily obtainable on neutralizing the free acid with any lithium base, e.g., the hydroxide or carbonate, followed by recovery of the salt from solution, which may be in water, alcohol or in an inert organic solvent, by methods known to the art. It is understood that the naphthenic acid used in the preparation of the lithium naphthenate can be the same as or different than the naphthenic acid component of the synergistic additive combination of this invention. It is preferred that the same naphthenic acid be used.

The organo-lead anti-knock agent can be any organolead compound capable of forming lead oxide in the cornbustion chamber. Such organo-lead compounds are well known to the art and include, for example, tetraethyl lead, tetramethyl lead, phenyl tn'methyl lead, ethyl trimethyl lead, diethyldimethyl lead, triethylmethyl lead, or mixtures thereof, the keto-lead compounds and solublized complexes thereof, etc. Other usable organo-lead compounds will be evident to those having ordinary skill in the art.

The aromatic-rich gasoline component of the compositions of this invention is any combustible hydrocarbon liquid of suitable volatility commonly employed as fuel for spark-ignition internal combustion engines. Such gasolines contain the paraffinic, naphthenic, olefinic, and aromatic hydrocarbon constituents. The minimum aromatic content of such gasolines is at least 20 volume percent and can reach up to 100 percent by volume. Generally, the aromatic content is between '20 and 80 volume percent. The boiling point of such combustible aromaticrich hydrocarbon liquids should be in the gasoline boiling range of from about 100 F. to about 500 F. and preferably in the range of from about 150 -F. to about 400 F. Such aromatic-rich gasolines can also contain anti-oxidants, stabilizers, dyes, anti-icing agents, lead scavenging agents, and/or other compounds which are commonly employed in leaded gasolines. The motor fuel, in accordance with this invention, for use in spark-ignition engines contains organo-lead anti-knock agents, preferably tetraethyl lead, equivalent to a concentration of from about 0.5 g. to about 6.34 g. of lead per gallon. The concentration of lead may be varied as is usual with the engine and its use.

In the following examples the effectiveness of the synergistic additive combination of naphthenic acid and lithium naphthenate as lead appreciator for improving the Research octane number and anti-knock characteris tics of leaded aromatic-rich gasolines having the prescribed aromatic content and Research octane number was determined by adding varying amounts of naphthenic acid and lithium naphthenate individually and in the prescribed additive combination proportions to the base fuels. The change in Research octane number for the resulting blends over each leaded base fuel was determined and the change reported as ARON. Each of the base fuels contained about 3 ml. of tetraethyl lead fluid per gallon. weight of 246;a saponification number of 22.8 mg. KOH/g.; an acid number of 224 mg. KOH/g.; and con tained 9.4% unsaponifiables. The lithium naphthenate containing about 2.5% lithium had an averagemolecular weight of about 150 and was added to the base fuels in amounts sufficient to'provide the appropriate amounts of lithium shown in the examples.

EXAMPLE I Table I Naphthem'c Lithium, acid,

Grams Volume ARON Added percent Added The data in Table I prove that naphthenic acid and lithium naphthenate when employed in the prescribed concentrations have a synergistic octane improvement effeet in leaded aromatic-rich base fuels.

The naphthenic acid had an equivalent EXAMPLE II In this example, the base fuel contained 41% by volume of aromatic hydrocarbons and 59% by volume of paratfinic and naphthenic hydrocarbons with a'leaded Research octane number of 101.1.

Table II Naphthenic Lithium, aci

Grams Volume ARON Added percent ded ' EXAMPLE III The base fuelemployed in this example had a leaded Research octane number of 102 and contained 39% by 7 volume of aromatic hydrocarbons, 10% by volume of olefinic hydrocarbons and 51% by volume of *parafiinic and naphthenic hydrocarbons.

Table III Naphthenic N Lithium, acid. a

Grams Volume ARON Added percent Added The data in Tables II andIII further confirm the synergistic action of naphthenic acid and lithium naphthenate in raising the Research octane number of leaded aromatic-rich gasolines.

Thus having described'the invention, what is claimed is:

. 1-. A leaded aromatic-rich gasoline having an aromatic hydrocarbon content of at least 20 volume percent and,

3. The gasoline of claim 2 wherein the amount of 10 3 009 792 naphthenic acid is from 0.1 to 1.0 volume percent, and the amount of lithium naphthenate provides from 0.25 to 1.5 grams of lithium per gallon.

4. A leaded aromatic-rich gasoline which contains about 3 ml. of tetraethyl lead, has an aromatic hydrocarbon content of from about 30 to about 45 volume percent and a minimum research octane number of 95, containing 6 a synergistic additive combination of from about 0.25 to about 1 volume percent of naphthenic acid and an amount of lithium naphthenate suflicient to provide from about 0.25 to about 1 g. of lithium per gallon of said gasoline whereby synergistic octane improvement of the research octane number of said gasoline is obtained.

References Cited in the file of this patent UNITED STATES PATENTS Eckert et al Nov. 21, 1961 3,013,869 Kissa Dec. 19, 1961 FOREIGN PATENTS 230,132 Australia May 15, 1959 571,921 Belgium Oct. 9, 1958 300,156 Great Britain Nov. 6, 1928 627,695 Canada Sept. 19, 1961 

1. A LEADED AROMATIC-RICH GASOLINE HAVING AN AROMATIC HYDROCARBON CONTENT OF AT LEAST 20 VOLUME PERCENT AND A MINIMUM RESEARCH OCTANE NUMBER OF 90 CONTAINING A SYNERGISTIC ADDITIVE COMBINATION OF (A) FROM 0.05 TO 1.0 VOLUME PERCENT OF MAPHTHENIC ACID AND (B) AND AMOUNT OF LITHIUM NAPTHENATE SUFFICIENT TO PROVIDE FROM 0.01 TO 2.5 GRAMS OF LITHIUM PER GALLON OF GASOLINE WHEREBY SYNERGISTIC OCATNE IMPROVEMENT OF THE RESEARCH OCTANE NUMBER OF THE GASOLINE IS OBTAINED. 